Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$212.75	4.616%	$222.5705	$222.57	$222.55	$222.60
Purchase #2	$142.84	8.147%	$154.4772	$154.48	$154.50	$154.50
Purchase #3	$105.99	11.550%	$118.2318	$118.23	$118.25	$118.20
Purchase #4	$79.95	12.738%	$90.134	$90.13	$90.15	$90.10
Purchase #5	$167.33	12.303%	$187.9166	$187.92	$187.90	$187.90
Purchase #6	$42.74	12.482%	$48.0748	$48.07	$48.05	$48.10
Purchase #7	$98.33	13.111%	$111.222	$111.22	$111.20	$111.20
7 purchase totals =	$849.93		$932.6269	$932.62	$932.60	$932.60